24 JURASSIC RHYNCHONELLIDS 
TYPE SPECIMEN. Lectotype, here designated, fig. 8, pl. 40 of Quenstedt (1871) 
from the ““ Malm gamma _”’ of Bosler, Germany. 
MATERIAL. 320 specimens from the collection of the University of Tubingen ; 
17 specimens collected by Dr. Enay from near Arinthod (Jura). 
DEsCRIPTION. External characters. The shell is equally biconvex and has a 
small, pointed, erect beak. The oval pedicle foramen is flanked by disjunct deltidial 
plates which show a characteristic thickening around the actual opening. Beak 
ridges and interarea are both well developed. 
The ornament consists of about 20 rounded ribs, as counted at the anterior margin, 
which mostly originate at the umbones although a few also arise by dichotomy. 
The well marked uniplication in the anterior commissure usually carries about six of 
these ribs. A distinctive feature of the species is the radial striae which can be seen 
only in the troughs between the ribs of well preserved specimens ; these striae are 
usually most easily observable toward the anterior margin. The better preserved 
specimens also show a concentric ornament of very fine growth lines, which are 
usually more apparent posteriorly ; growth lamellae are rarely developed. 
The shell of many of the broken and worn specimens is seen to be of a very fibrous 
character ; whether this is its original condition or the result of post-burial recrys- 
tallisation, as evidenced by the loss of the fine detail, is not known. Although the 
shell fibres and the radial striae superficially resemble one another, the striae may be 
differentiated by the fact that they are more individually distinct and occur only in 
the troughs, whereas the fibres appear as a compact mass and may be visible on any 
part of the shell. If the top layer of the shell has been removed so that the fibrous 
condition is visible, this inevitably means that the striae will have been obliterated. 
DIMENSIONS OF FIGURED SPECIMENS. 
length thickness width 
I-00 cm 0:68 cm I-00 cm 
0:87 cm 0-59 cm 0-87 cm 
1:27 cm 0:84 cm 1:26 cm 
Internal characters. Pedicle valve. The shell is quite thick and the dental 
lamellae are relatively well developed. The teeth are inserted vertically into the 
sockets, as seen in transverse section. 
Brachial valve. There is no median septum or ridge developed ; other details 
are as in generic description. 
DISTRIBUTION. The species is known from the Swabian and Franconian Jura, 
Poland and the central French Jura. The only other record is that of Jacob and 
Fallot (1913) from the “‘ Portlandien supérieur ”’ of Chomérac (Ardéche). 
OccuRRENCE. The author has not collected the species and it is only briefly 
recorded in the literature. Quenstedt (1871) noted that it occurred with Terebratula 
lacunosa. The horizon cited by Jacob and Fallot appears to yield a very varied 
rhynchonellid fauna, some of which is almost certainly referable to the genus 
Lacunosella Wisniewska. The material of Dr. Enay came from a fine grained marl 
from which specimens of Acanthorhynchia (Echinirhynchia) lorioli were also obtained. 
